Why @constCast need explict type in 0.14?

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1 
test "const cast" {
    // myfn(@constCast(&.{.count = 0})); //does not work in zig 0.14 anymore
    myfn(@constCast(&SuperLongName______________________________Struct{.count = 0}));
    constArgFn(&.{.count = 0});

}

const SuperLongName______________________________Struct = struct {
    count: usize,
};


fn myfn(arg: *SuperLongName______________________________Struct) void {
    std.debug.print("count={}\n", .{arg.count});
}


fn constArgFn(arg: *const SuperLongName______________________________Struct) void {
    std.debug.print("count={}\n", .{arg.count});
}
2

I believe this is the relevant part of the release notes:

Remove Anonymous Struct Types, Unify Tuples

3 Likes
3

By the way, that’s illegal behavior. In your code the SuperLongName is a const temporary. If you want it to be mutable, put it in a var.

4

Im pretty sure its ok to @constCast temporaries. It would be illigal behavior only if you try to actually mutate value. Here is example of doing it in compiler source code:

5

Sure but I assumed in the non-toy code OP would be mutating the value. Otherwise they could just change the pointer type to const and wouldn’t need the cast in the first place.

6

thx for the advice.
since @constCast was provided, there is a need for it, i think this is a place.

7

thx.
not notice the behavior before.
now i find that, mutation is ill only in safe or debug mode.